Peel the oranges with a vegetable peeler or grater and cut the peel into small pieces.
In a blender or small food processor, combine the orange peel, juice from the oranges, garlic, oil, salt, and chipotle peppers. Blend it until smooth. Reserve half the sauce.
With a long-toothed fork, poke holes in the pork. Place the pork inside a plastic bag or a deep container, pour the sauce over the pork, close the bag very tightly or cover the container and let it marinate in the refrigerator for at least two hours or overnight.
Place the pork on a baking rack (dispose of the marinating sauce).
Pour a cup of water into the base of the baking dish. Roast the pork at 325° F for 1-1/2 to 2 hours or until the meat thermometer registers 150° F in the center of the meat. Check the pork half way through cooking time to add more water to the baking dish if necessary. If too brown, cover with aluminum foil for remainder of cooking time.
Upon extracting the pork from the oven, let it rest, still covered with aluminum foil for 10 minutes before slicing. Heat up the reserved sauce in a small saucepan for 5 minutes or until it has lightly reduced.